Tag Archives: tunicata

Door #15: The eye of the beholder

It’s funny to see the different reactions to fresh material that comes in to the museum;  the exhibition team had  received some kelp that will be pressed and dried for the new exhibitions (opening fall 2019), and I ducked in to secure some of the fauna sitting on the kelp before it was scraped off and discarded. For the botanists, the animals were merely a distraction that needed to be removed so that they could deal with the kelp, whilst I was trying to avoid too much algae in the sample as it messes up the fixation of the animals.

I chose the right shirt for the day- it’s full of nudibranchs! (photo: L. Martell)


I then spirited my loot into the lab, and set up camp.

Count me in amongst the people who stare at lumps of seaweed.


Who’s there? The whole lump is ~12 cm.

How many animals do you see here? Which ones appeal to you?

I have made a quick annotation of some of the biota here:

Note that these are just some of the critters present…! (photo: K. Kongshavn)

Let’s go closer on a small piece of algae:

Now, what do you see? (photo: K. Kongshavn)

For Luis, the first thing to catch the eye was (of course) the Hydrozoa

Hydrozoans (the christmas light looking strings), encrusting bryozoans (the flat, encrusting growth on on the algae – you might also know them as moss animals), and some white, spiralling polychaete tubes  (photo: K. Kongshavn)

Did you spot the sea hare (Aplysia punctata?) Look a bit above the middle of the photo of the tiny aquarium with the black background. Do you see a red-pink blob?

Hello, Aplysia punctata! (photo: K. Kongshavn)

There were also several other sea slugs that I have handed over to Cessa for inclusion in the sea slugs of Southern Norway project, here are a few:

Then there were the shelled gastropods:

The brittle star from the earlier image – this is a Ophiopholis aculeata, the crevice sea star (photo: K. Kongshavn)

In fact, they both are Ophiopholis aculeata (in Norwegian we call them “chameleon brittle stars” – they live up to the name!), one of the very common species around here. (photo: K. Kongshavn)

One of the colonial ascidian tunicates (and some of the ever present bryozoa just below it) (photo: K. Kongshavn)

Most of these animals will be barcoded, and will help build our reference library for species that occur in Norway. I also hope that they may have helped open your eyes to some of the more inconspicuous creatures that live just beneath the surface?

2019 will see the start of a new species taxonomy project where we will explore the invertebrate fauna of shallow-water rocky shores, so there will be many more posts like this to come!


Door #13: Time for rejuvenation

Some of the fundamental existential impacts of the solar cycle were certainly understood by the Neolithic people who built Newgrange and were able to align the gigantic construction with the position of the sun rise at winter solstice. It was a point of return in “the wheel of time”, the annual cycle of “ageing, rebirth, and rejuvenation of Nature”. But how living individuals reproduce and come into being was a mystery right up to modern times. The Roman writer in natural history, Pliny (ca 70 AD), for instance stated that: “…after six months’ duration , frogs melt away into slime, though no one ever sees how it is done; after which they come to life again in the water during the spring, just as they were before. This is affected by some occult operation of Nature, and happens regularly every year. Mussels, also, and scallops are produced in the sand by the spontaneous operations of nature.”

Although the famous experiments by Francesco Redi had refuted some ideas about “spontaneous generation” in the mid 16-hundreds, the concept was still an important part of Lamarck’s theory of evolution that was opposed by his colleague Cuvier. Birth, of course, has also been a subject of discussions when pondering the mysteries of the Mary cult: was it really a case of parthenogenesis? What is really going on in the making of a body – the “process of incarnation”?


Botryllus schlosseri (photo: K. Kongshavn)

Botryllus schlosseri, the “golden star tunicate”, is a common species on Atlantic coasts and recently has expanded its distributions to other seas as a result of human marine travelling. Researchers at the University of Bergen (Delsuc et al 2006) found that the tunicates belong to an evolutionary lineage that is the closest to vertebrates (including humans). B. schlosseri is relatively easy to keep in aquaria and has taught us a lot about reproduction and life cycles.

The similarity between the tunicates and the vertebrates are only apparent in the early stages of tunicate life. The larvae have a body with a tail containing the “chorda”, and a dorsal nerve tube, – both unique characteristic features of the Chordate animals (see figure 1A in in Voskoboynik el al. 2013). But these similarities disappear within a few hours when the free swimming larva has settled on some surface substrate and started the metamorphosis into the sack like body of an adult tunicate with a filter feeding gut. The larva was the result of sexual reproduction, the merged genetic material from sperm and egg. However, the metamorphosed individual will soon begin to reproduce asexually by budding off a copy of itself in a neighbouring position. The results of such multiplications are clusters of two to 12 genetically identical individuals in a star like pattern. These individuals, called zooids, are active for relatively short time, about a week at 19 oC, until they become inactive and gradually are reabsorbed by other cells in the colony while being replaced by new zooids. This sort of programmed cell death is called apoptosis and researches believe that studies of B. schlosseri can reveal some of what is going on with ageing and death of cells. It has been estimated that in an adult human body there is apoptosis of about 50 to 70 billion cells per day. Fortunately there is also renewal of cells, like in the growing colony of Botryllus. Very interesting things may happen if the zooids from different larvae are meeting up at the margins of two colonies with the so-called ampullae. Botryllus has a self-recognition system that is controlled by just one gene, but the gene occurs in many variants (alleles). If the alleles from two colonies are compatible, the blood vessel systems of the two colonies may grow together so that one colony is actually formed by zooids with different genetics. This is somewhat analogous to what happens between mother and child in the mammalian placenta. If the compatibility of two colonies is bad, they will “fight” each other in an inflammatory immune reaction. Such processes have special interest with respect to understanding immune systems and the outcome of organ transplantation.

It takes about 3-4 weeks for a colony to become sexually mature so that egg and sperm may be released in turn, avoiding self-fertilization. The duration of a colony is believed to be about 12 to 18 months in Norwegian waters (Moen & Svendsen 2008).

The reproduction system of B. schlosseri is just one of many different reproduction systems of animals. Where does individuality begin and stop? Would a zooid greet its neighbour with “Merry Christmas, I!”?

Suggested reading:

Delsuc et al. (2006). Tunicates and not cephalochordates are the closest living relatives of vertebrates. Nature: 439:965-968.

Manni et al (2007). Botryllus schlosseri: A model ascidian for the study of asexual reproduction. Developmental Dynamics 236(2): 335-352.

Moen & Svendsen (2008) Dyreliv i havet. KOM Forlag.

Tiozzo et al. (2006). Programmed cell death in vegetative development: Apoptosis during the colonial life cycle of the ascidian Botryllus schlosseri. Tissue and Cell 38 (3): 193-201

Voskoboynik et al. (2013) The genome sequence of the colonial chordate, Botryllus schlosseri Elife. DOI: 10.7554/eLife.00569.001